The Federal Aviation Administration (FAA) has issued a directive requiring all aircraft operators in the United States using Pratt & Whitney PW4000 engines to test them before flying.

“Tonight, the FAA issued an emergency airworthiness directive that requires US aircraft operators equipped with certain Pratt & Whitney PW4000 engines to test those engines before further flight,” the regulator’s website said.

The FAA said operators must conduct inspections to detect cracks on the inside of hollow fan blades and surfaces that are not visible upon inspection.

On Saturday, Fox News previously reported that due to an engine malfunction, the debris of a United Airlines passenger, Boeing 777, fell in a residential area near the American city of Denver (Colorado). The plane returned safely to Denver shortly after departure.

There is no information on casualties on board or as a result of falling debris. The American airline United Airlines has temporarily suspended flights of its 24 aircraft of this type.